For many years, a number of modulation techniques have been used to transfer data from a source to a destination. One class of modulation technique is referred to as multi-carrier modulation (MCM). In accordance with multi-carrier modulation (MCM), data is transmitted in parallel by way of a plurality of carriers. In a multi-carrier modulation (MCM) system, data is first organized in frames for transmission in parallel via the plurality of carriers. Then, the framed data is modulated onto respective carriers for transmission. Examples of multi-carrier modulation (MCM) include frequency division multiplexing (FDM), orthogonal frequency division multiplexing (OFDM), and multi-carrier code-division multiple access (CDMA).
Of particular interest to the invention is the orthogonal frequency division multiplexing (OFDM). However, although orthogonal frequency division multiplexing (OFDM) will serve to illustrate the invention, it shall be understood that the principles of the invention can be applied to other multi-carrier modulation systems, such as frequency division multiplexing (FDM) and multi-carrier code-division multiple access (CDMA). In an orthogonal frequency division multiplexing (OFDM) system, a frame of data is applied to an Inverse Fast Fourier Transform (IFFT). The Inverse Fast Fourier Transform (IFFT) modulates the framed data to respective carriers.
An advantage of orthogonal frequency division multiplexing (OFDM) stems from the fact that adjacent carriers overlap in frequency and the carriers are orthogonal with respective to each other. The overlapping of adjacent carriers is advantageous because more carriers can be used within a given bandwidth, and therefore the data throughput is generally higher within the given bandwidth. The orthogonality of the carriers is advantageous because it reduces inter carrier interference (ICI). That is, because in an orthogonal system a carrier's frequency response is at approximately zero amplitude at the maximum amplitude of all other carriers, the likelihood of interference between carriers is reduced.
Since the carriers of an orthogonal frequency division multiplexing (OFDM) system are adjacent and overlap, the carriers as a whole occupy a continuous bandwidth. Often, this continuous bandwidth has to be shared with one or more other communications systems. Thus, these other one or more communications systems occupy a portion of the continuous bandwidth of an orthogonal frequency division multiplexing (OFDM) signal. Therefore, it is often desirable to shape the frequency spectrum of an orthogonal frequency division multiplexing (OFDM) signal so that it does not affect the operation of the other one or more communications systems occupying the same continuous bandwidth.
Thus, there is a need for a system and method of signal wave shaping for spectrum control of an orthogonal frequency division multiplexing (OFDM) signal to prevent interference with other communication systems that occupy the same bandwidth, as well as perform other desired functions. There is also a further need for a system and method of signal wave shaping for spectrum control of an orthogonal frequency division multiplexing (OFDM) that is adaptive (i.e. programmable) in order to change its frequency response to compensate for change in the bandwidth environment and also to make the system versatile. Such a system and method are described herein in accordance with the invention.